Radiation imaging apparatus and method of controlling the same

ABSTRACT

A radiation imaging apparatus detects the density distribution of an image formed by a radiopaque dye from each of two images obtained by radiation imaging. The apparatus predicts the moving speed of the image formed by the radiopaque dye based on the moving amount of the detected density distribution and the interval between the radiographing times of the two images, and determines the next timing of radiation imaging based on the predicted moving speed and the detected density distribution. A radiation imaging apparatus detects the density distribution of a radiopaque dye in an image obtained by X-ray radiation imaging and predicts the moving speed of the radiopaque dye based on the change amount of the density distribution. The radiation imaging apparatus determines the X-ray irradiation timing based on the predicted radiopaque dye moving speed, the detected radiopaque dye density distribution, and a predetermined radiopaque dye density.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a radiation imaging apparatus forperforming radiation imaging using a radiopaque dye, and a method ofcontrolling the same.

2. Description of the Related Art

Angiography by an X-ray diagnostic imaging apparatus is done using aradiopaque dye. When blood vessels in which a radiopaque dye is injectedare radiographed by X-ray radiation imaging, an X-ray absorptiondifference is generated between the blood vessels and other tissues, andthe blood vessel form or blood flow state can be visualized moreclearly. This allows the doctor to make a more correct diagnosis ortreatment.

A common method of angiography using a radiopaque dye is DSA (DigitalSubtraction Angiography). In DSA, an object is radiographed by X-rayradiation imaging to obtain an image before radiopaque dye injection.This image is called a mask image. Next, a radiopaque dye is injectedinto blood vessels. The object is radiographed by X-ray imaging toobtain an image after radiopaque dye injection. This image is called acontrast image. The difference between the mask image and the contrastimage is calculated, and the background including bones and organs iserased, thereby obtaining an angiographic image containing only a bloodvessel image.

To generate an angiographic image containing only blood vessels,continuous images are obtained by radiographing the movement of aradiopaque dye over a plurality of frames, and the peak value isobtained at each pixel position. Based on the peak value of each pixel,images with the highest radiopaque dye density are composited togenerate a blood vessel angiographic image.

The irradiation for X-ray imaging is performed at a preset fixed framerate. Generally, a technician sets the frame rate in accordance with thebody part to be radiographed. There also exists an apparatus whichallows a technician to manually change the frame rate during X-rayimaging.

A technique of determining the frame rate of X-ray imaging is disclosedin Japanese Patent Laid-Open No. 5-192319 (to be referred to as patentreference 1 hereinafter). Patent reference 1 proposes an X-raydiagnostic apparatus which controls X-ray irradiation in accordance witha change in an object. This apparatus raises the frame rate upondetermining that a radiopaque dye enters the irradiation field.

However, the prior art has the following problems.

The amount of use of the radiopaque dye is preferably small in order tosuppress the side effect. However, when the amount of use is small, itis necessary to perform imaging at a high frame rate without failing toradiograph images. This leads to excess imaging and an increase in theirradiation dose at a portion with a slow blood flow. If imaging is doneat a low frame rate to prevent excess irradiation, an imaging failureoccurs at a portion with a fast blood flow, and the obtainedangiographic image contains breaks in the blood vessels. That is, excessor deficient irradiation occurs depending on the moving speed of theradiopaque dye.

To manually deal with a change in the blood flow velocity, thetechnician raises the frame rate when the blood flow velocity increasesand lowers the frame rate when the blood flow velocity decreases byoperating a user interface (UI) while visually observing, on a monitor,the blood vessel image that is being radiographed. In this method, thereaction speed of human eye (human sensation) affects the frame rateadjustment. It is therefore difficult to avoid excess imaging or imagingfailure.

In patent reference 1, it is possible to suppress the total irradiationdose of a patient by limiting the high frame rate period to, forexample, a period when the radiopaque dye is present in the irradiationfield. When determining that the radiopaque dye enters the irradiationfield, imaging using a high frame rate is performed. This prevents animaging failure but cannot solve the problem of the high irradiationdose caused by excess imaging at a portion with a slow blood flow.

SUMMARY OF THE INVENTION

According to a typical aspect of the present invention, there areprovided a radiation imaging apparatus capable of acquiring aradiographic image by appropriate irradiation while suppressing theirradiation dose and the radiopaque dye injection amount by controllingthe irradiation timing of radiation in accordance with a change in theradiopaque dye moving speed, and a method of controlling the same.

According to one aspect of the present invention, there is provided aradiation imaging apparatus comprising:

a detection unit adapted to detect a density distribution of an imageformed by a radiopaque dye from an image obtained by radiation imaging;

a prediction unit adapted to calculate a moving speed of the imageformed by the radiopaque dye on the basis of a moving amount of thedensity distribution detected by the detection unit in two imagesobtained by radiation imaging and an interval between radiographingtimes of the two images; and

a determination unit adapted to determine a next timing of radiationimaging on the basis of the moving speed calculated by the predictionunit and the density distribution detected by the detection unit.

Also, according to another aspect of the present invention, there isprovided a method of controlling a radiation imaging apparatus,comprising:

a detection step of detecting a density distribution of an image formedby a radiopaque dye from an image obtained by radiation imaging;

a prediction step of calculating a moving speed of the image formed bythe radiopaque dye on the basis of a moving amount of the densitydistribution detected in the detection step in two images obtained byradiation imaging and an interval between radiographing times of the twoimages; and

a determination step of determining a next timing of radiation imagingon the basis of the moving speed calculated in the prediction step andthe density distribution detected in the detection step.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of the arrangement of anX-ray diagnostic imaging apparatus according to an embodiment;

FIG. 2 is a block diagram showing an example of the functionalarrangement of the system controller of the X-ray diagnostic imagingapparatus according to the embodiment;

FIG. 3 is a flowchart illustrating an X-ray irradiation processaccording to the first embodiment;

FIG. 4 is a flowchart illustrating a process of determining the X-rayirradiation timing by the system controller according to the firstembodiment;

FIG. 5 is a view showing an example of a blood vessel image radiographedby the X-ray diagnostic imaging apparatus;

FIG. 6 is a graph showing the relationship between the moving distanceand density of a radiopaque dye and the X-ray irradiation timingaccording to the first embodiment;

FIG. 7 is a flowchart illustrating a process of determining the X-rayirradiation timing by a system controller according to the secondembodiment; and

FIG. 8 is a graph showing the relationship between the moving distanceand density of a radiopaque dye and the X-ray irradiation timingaccording to the second embodiment.

DESCRIPTION OF THE EMBODIMENTS

Exemplary embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

First Embodiment

FIG. 1 is a block diagram showing an example of the arrangement of anX-ray diagnostic imaging apparatus according to this embodiment. In thisembodiment, an X-ray diagnostic imaging apparatus for performing X-rayimaging will be exemplified as a radiation imaging apparatus forperforming radiation imaging. In the X-ray diagnostic imaging apparatus,a holding unit 101 has an X-ray generation unit (X-ray tube) 102stationarily supported at an end as an X-ray generation source, and anX-ray detection unit 103 stationarily supported at the other end as anX-ray detection means. With this structure, the holding unit 101stationarily supports the X-ray generation unit 102 and the X-raydetection unit 103, which oppose each other. A bed 104 is providedbetween the X-ray generation unit 102 and the X-ray detection unit 103.The bed 104 has a top plate (not shown) and leg portions (not shown)that support the top plate. An object 105, that is, a patient is placedon the top plate. The top plate is movable in necessary directions, forexample, vertically and horizontally.

Each of the top plate (not shown) of the bed 104 and the holding unit101 has a motor (not shown) and a position sensor (not shown). Themotors and position sensors are connected to a machine controller 106.The machine controller 106 controls the motors in accordance with sensorinformation from the position sensors and drives the top plate of thebed 104 and the holding unit 101 so that they have a required positionalrelationship.

The X-ray generation unit 102 is connected to a high voltage generationunit 107. The X-ray generation unit 102 receives a necessary voltagefrom the high voltage generation unit 107 and irradiates the object 105with X-rays. The high voltage generation unit 107 is connected to anX-ray controller 108. The X-ray controller 108 controls the high voltagegeneration unit 107, thereby controlling the dose of X-rays to be outputfrom the X-ray generation unit 102 during imaging or fluorography. Themachine controller 106 and X-ray controller 108 are connected to asystem controller 109 and controlled by it.

The X-ray detection unit 103 is connected to an image reading unit 111which reads out image data from the X-ray detection unit 103. The imagereading unit 111 is connected to an image processing unit 112. The imageprocessing unit 112 processes the image data read by the image readingunit 111.

A display unit 113 is connected to the image processing unit 112 and anangiographic image generation unit 117 and displays image data processedby the image processing unit 112 or an image based on angiographic imagedata generated by the angiographic image generation unit 117. Thedisplay unit 113 also displays object information (e.g., name, age, sex,length, weight, and imaging or fluoroscopy target body part) and imagingand fluoroscopic conditions including X-ray conditions.

Various kinds of controllers such as the machine controller 106 andX-ray controller 108, an input unit 110, the image processing unit 112,and an image difference calculation unit 116 are connected to the systemcontroller 109. The input unit 110 includes a keyboard, mouse, touchpanel, membrane buttons, and joystick, and an irradiation switch or footpedal to give a trigger to start or stop irradiation. The imageprocessing unit 112 executes image processing such as gamma correctionor noise reduction. The image difference calculation unit 116 generatesan angiographic image. Note that the imaging and fluoroscopic conditionsand the object information (e.g., name, age, sex, length, weight, andimaging or fluoroscopy target body part) are input from the input unit110.

An injector 114 is a tool for injecting a radiopaque dye in a bloodvessel of the object 105. The radiopaque dye is injected in apredetermined part of the object 105 in accordance with the diagnosticpart. A mask image holding unit 115, image difference calculation unit116, and angiographic image generation unit 117 are components to beused for angiography using a radiopaque dye. The mask image holding unit115 holds, in a storage unit (e.g., RAM 202), image data (mask image)before radiopaque dye injection which is processed by the imageprocessing unit 112. The image difference calculation unit 116 executesa subtraction process of calculating the difference between the maskimage obtained from the mask image holding unit 115 and an image(contrast image) after radiopaque dye injection obtained from the imageprocessing unit 112. The angiographic image generation unit 117generates an angiographic image based on the image data obtained by theimage difference calculation unit 116.

FIG. 2 is a block diagram showing an example of the functionalarrangement of the system controller 109 of the X-ray diagnostic imagingapparatus shown in FIG. 1.

The system controller 109 includes a CPU 201 which implements theprocedure of flowcharts to be described later, the RAM 202 functioningas the main memory or work memory of the CPU 201, and a ROM 203 storingprograms. The ROM 203 stores programs which cause the CPU 201 tofunction as a radiopaque dye density distribution detection unit 204,radiopaque dye moving speed prediction unit 205, X-ray irradiationtiming determination unit 206, and X-ray irradiation timing managementunit 207.

The radiopaque dye density distribution detection unit 204 analyzesimage data obtained from the image processing unit 112, therebydetecting the radiopaque dye density distribution in the image. Theradiopaque dye moving speed prediction unit 205 calculates the movingspeed of an image formed by the radiopaque dye based on the amount ofchange (moving amount) of the radiopaque dye density distributionbetween two images obtained from the radiopaque dye density distributiondetection unit 204. This speed is called the predicted moving speed ofthe radiopaque dye. More specifically, the radiopaque dye moving speedprediction unit 205 calculates the moving speed of the image formed bythe radiopaque dye based on the amount of movement of the densitydistribution between two images obtained upon X-ray imaging and theinterval between the radiographing times of the images.

The X-ray irradiation timing determination unit 206 determines the X-rayirradiation timing based on a predetermined radiopaque dye density, theradiopaque dye density distribution detected by the radiopaque dyedensity distribution detection unit 204, and the predicted moving speedof the radiopaque dye calculated by the radiopaque dye moving speedprediction unit 205. Note that the predetermined radiopaque dye densityis a radiopaque dye density value necessary for generating anangiographic image in consideration of noise and the like. The processof the X-ray irradiation timing determination unit 206 will be describedlater in detail with reference to the flowchart in FIG. 4.

The X-ray irradiation timing management unit 207 has a function ofholding the X-ray irradiation timing in a storage unit (e.g., RAM 202)and manages the X-ray irradiation timing. In accordance with the valueheld by the X-ray irradiation timing management unit 207, the X-raycontroller 108 is controlled to perform X-ray irradiation.

FIG. 3 is a flowchart illustrating the operation of the X-ray diagnosticimaging apparatus according to the first embodiment.

Step S301 is the start point of the process. In step S302, the CPU 201determines whether a trigger to start X-ray irradiation is given. Thetrigger to start X-ray irradiation is given by, for example, pressingthe foot pedal or irradiation switch of the input unit 110. If it isdetermined that the trigger to start X-ray irradiation is given, theprocess advances to step S303. Otherwise, the process returns to stepS302. That is, in step S302, the process waits until the trigger tostart irradiation is detected by polling or the like. Upon detecting thetrigger to start irradiation, the process advances to step S303.

In step S303, the X-ray irradiation timing management unit 207 sends aninstruction to the X-ray controller 108 to perform X-ray irradiationbased on the X-ray irradiation timing held in the storage unit (the RAM202 in this embodiment). Note that as the initial value of the X-rayirradiation timing, a preset default value or a value set by atechnician before the operation is held.

In step S304, the radiopaque dye density distribution detection unit 204detects the radiopaque dye density distribution for the radiographedimage. The density distribution is detected by image processing. Morespecifically, the density distribution is detected by calculating theamount of change of the luminance value of each pixel that was, forexample, formerly bright and abruptly darkened. That is, the radiopaquedye density distribution is obtained by specifying the existence rangeof the radiopaque dye in the image based on the change in the luminancevalue of each pixel and detecting the density distribution in theexistence range of the radiopaque dye.

In step S305, the radiopaque dye moving speed prediction unit 205acquires the point with the highest radiopaque dye density from each ofthe radiopaque dye density distribution in the latest radiographed imagedetected in step S304 and the radiopaque dye density distribution in theimmediately preceding radiographed image. Based on the moving distanceof the point with the highest density and the interval between thedensity distribution detection times (the interval between theradiographing times of the two images), the radiopaque dye moving speedprediction unit 205 calculates the moving speed of the radiopaque dye asthe next predicted moving speed of the radiopaque dye. Note that themoving distance is the distance along the image of the radiopaque dye.For example, if P1min moves to P1max in a blood vessel image shown inFIG. 5, the distance along the curve of the blood vessel image iscalculated as the moving distance.

In step S306, the X-ray irradiation timing determination unit 206determines the X-ray irradiation timing. The X-ray irradiation timing isdetermined based on the information of the radiopaque dye densitydistribution detected in step S304, the predicted moving speed of theradiopaque dye calculated in step S305, and a predetermined radiopaquedye density necessary for generating an angiographic image. That is, theX-ray irradiation timing is updated as needed as the moving speed of theradiopaque dye varies. This process will be described later in detailwith reference to the flowchart in FIG. 4.

In step S307, the CPU 201 determines whether a trigger for X-rayirradiation is given. The trigger for X-ray irradiation is given bypressing the foot pedal or irradiation switch, as in step S302. If it isdetermined that the trigger for irradiation is given, the processreturns to step S303. Otherwise, the process advances to step S308. StepS308 is the end point of the algorithm.

FIG. 4 is a flowchart illustrating a process of causing the X-rayirradiation timing determination unit 206 to determine the X-rayirradiation timing (the process in step S306 of FIG. 3). The processsequence will be explained also using the graph in FIG. 6 which showsthe relationship between the moving distance and density of a radiopaquedye and the X-ray irradiation timing.

Let fi (P) be the radiopaque dye density of a point P at time Ti, and gi(P) be the predicted radiopaque dye density of the point P at futuretime Tj. The density gi (P) is predicted based on fi (P) assuming thatthe radiopaque dye density distribution does not relatively change in ashort time. The radiographing time of the latest image is defined as T1.

Step S401 is the start point of the algorithm. In step S402, the X-rayirradiation timing determination unit 206 calculates an end point P1minand a leading point P1max of a blood vessel image where a radiopaque dyedensity f1 (P) of the point P at the time T1 exceeds the predeterminedradiopaque dye density necessary for generating an angiographic image.The end point and leading point are the end point and start point of theradiopaque dye in a blood vessel which satisfy the following condition.That is, the minimum value P1min and maximum value P1max of the point Pshown in FIG. 6, which satisfy

f1(P)>predetermined radiopaque dye density are calculated.

In step S403, the X-ray irradiation timing determination unit 206determines the X-ray irradiation timing based on the predicted movingspeed of the radiopaque dye calculated in step S305 of FIG. 3, and themoving distance from the point P1min to the point P1max calculated instep S402. The X-ray irradiation timing is the timing at which P1minreaches P1max when the radiopaque dye moves at the predicted movingspeed. Hence, the next X-ray irradiation timing T2 is given by

T2=T1+(P1max−P1min)/predicted moving speed

That is, the timing at which f1 (P) in FIG. 6 matches g1 (P) isdetermined as the X-ray irradiation timing.

In step S404, the X-ray irradiation timing determination unit 206 setsthe X-ray irradiation timing calculated in step S403 in the X-rayirradiation timing management unit 207. Step S405 is the end point ofthe algorithm.

FIG. 5 is a view showing a blood vessel image radiographed by the X-raydiagnostic imaging apparatus. The blood is assumed to flow from a pointPstart to a point Pend.

FIG. 6 will be described next in detail. FIG. 6 is a graph showing therelationship between the moving distance and density of the radiopaquedye and the X-ray irradiation timing according to the first embodiment.Referring to FIG. 6, the ordinate represents the density of theradiopaque dye, and the abscissa represents the moving distance of theblood flow from the point Pstart to the point Pend in FIG. 5.Additionally,

f1 (P) is the actual radiopaque dye density distribution of the point Pat the time T1,

g1 (P) is the predicted radiopaque dye density distribution of the pointP at the time T2, which is predicted at the time T1,

f2 (P) is the actual radiopaque dye density distribution of the point Pat the time T2,

g2 (P) is the predicted radiopaque dye density distribution of the pointP at time T3, which is predicted at the time T2,

P1min is the minimum value (end point) that satisfies “f1(P)≧predetermined radiopaque dye density”,

P1max is the maximum value (leading point) that satisfies “f1(P)≧predetermined radiopaque dye density”,

P2min is the minimum value (end point) that satisfies “f2(P)≧predetermined radiopaque dye density”, and

P2max is the maximum value (leading point) that satisfies “f2(P)≧predetermined radiopaque dye density”.

However, g1 (P) and g2( P) are predicted based on f1 (P) and f2 (P),respectively, assuming that the radiopaque dye density distribution doesnot relatively change in a short time. The X-ray irradiation timingdetermination unit 206 of the first embodiment determines the next X-rayirradiation timing based on the moving speed calculated by theradiopaque dye moving speed prediction unit 205 and the radiopaque dyedensity distribution detected by the radiopaque dye density distributiondetection unit 204. For example, the X-ray irradiation timingdetermination unit 206 determines the next timing of radiation imagingso that an image having a predetermined radiopaque dye density or morein the image obtained by the latest radiation imaging is jointed withthat in the image to be obtained by the next radiation imaging. That is,the next timing of radiation imaging is determined such that the imageof f1 (P) and the image of g1 (P) are jointed at the position of thepredetermined radiopaque dye density. In this embodiment, the nexttiming of radiation imaging is determined such that the images arejointed at the position of the minimum and necessary radiopaque dyedensity for generating an angiographic image as the predeterminedradiopaque dye density, that is, such that P1min changes to P1max. Atand near the timing when the radiopaque dye enters the screen, Pminmatches Pstart. Similarly, at the timing when the radiopaque dye leavesthe screen, Pmax matches Pend.

In the first embodiment, the radiopaque dye density distributiondetection method of the radiopaque dye density distribution detectionunit 204 is not limited to that in step S304 of FIG. 3. The predictedradiopaque dye moving speed calculation method of the radiopaque dyemoving speed prediction unit 205 is not limited to that in step S305 ofFIG. 3 (calculating the moving distance based on the point with thehighest radiopaque dye density between two images and calculating thepredicted moving speed). For example, a method of calculating the movingdistance of “the leading point of the radiopaque dye image having thepredetermined radiopaque dye density or more” between two images andcalculating the predicted moving speed may be employed.

Second Embodiment

X-ray irradiation control of a system controller 109 according to thesecond embodiment is the same as in the first embodiment (the processillustrated by the flowchart in FIG. 3). The different point is aprocess of causing an X-ray irradiation timing determination unit 206 todetermine the X-ray irradiation timing (the process in step S306 of FIG.3).

FIG. 7 is a flowchart illustrating the process of causing the X-rayirradiation timing determination unit 206 to determine the X-rayirradiation timing (the process in step S306 of FIG. 3) according to thesecond embodiment. The process sequence will be explained also using thegraph in FIG. 8 which shows the relationship between the moving distanceand density of a radiopaque dye and the X-ray irradiation timing. FIG. 8will be described later in detail.

Let fi (P) be the radiopaque dye density of a point P at time Ti, and gi(P) be the predicted radiopaque dye density of the point P at futuretime Tj. The density gi (P) is predicted based on fi (P) assuming thatthe radiopaque dye density distribution does not relatively change in ashort time. The radiographing time of the latest image is defined as T1.

Step S701 is the start point of the algorithm. In step S702, the X-rayirradiation timing determination unit 206 calculates an end point P1minof a blood vessel image where a radiopaque dye density f1 (P) of thepoint P at the time T1 exceeds the predetermined radiopaque dye densitynecessary for generating an angiographic image. The end point is the endpoint of the radiopaque dye in a blood vessel which satisfy theabove-described condition. That is, the minimum value P1min shown inFIG. 8, which satisfies

f1(P)≧predetermined radiopaque dye density is calculated.

In step S703, the X-ray irradiation timing determination unit 206calculates P1max. P1max is the leading point of the blood vessel imagewhere the sum of the radiopaque dye density f1 (P) of the point P at thetime T1 and a predicted radiopaque dye density g1 (P) of the point P attime T2, which is predicted at the time T1, exceeds the predeterminedradiopaque dye density. The leading point is the start point of theradiopaque dye in the blood vessel which satisfies the above-describedcondition. That is, the maximum value P1max shown in FIG. 8, whichsatisfies

f1(P)+g1(P)

>predetermined radiopaque dye density

(for f1(P) >0) is calculated.

In step S704, the X-ray irradiation timing determination unit 206determines the X-ray irradiation timing. The X-ray irradiation timing isdetermined using the predicted moving speed of the radiopaque dyecalculated in step S305 of FIG. 3, and the moving distance from thepoint P1min calculated in step S702 to the point P1max calculated instep S703. The X-ray irradiation timing is the timing at which P1minreaches P1max when the radiopaque dye moves at the predicted movingspeed. Hence, the next X-ray irradiation timing T2 is given by

T2=T1+(P1max−P1min)/predicted moving speed

That is, the timing at which f1(P) in FIG. 8 matches g1(P) is determinedas the X-ray irradiation timing.

In step S705, the X-ray irradiation timing determination unit 206 setsthe X-ray irradiation timing calculated in step S704 in an X-rayirradiation timing management unit 207. Step S706 is the end point ofthe algorithm.

FIG. 8 is a graph showing the relationship between the moving distanceand density of the radiopaque dye and the X-ray irradiation timingaccording to the second embodiment. Referring to FIG. 8, the ordinaterepresents the density of the radiopaque dye, and the abscissarepresents the moving distance of the blood flow from a point Pstart toa point Pend in FIG. 5. Additionally,

f1 (P) is the actual radiopaque dye density distribution of the point Pat the time T1,

g1 (P) is the predicted radiopaque dye density distribution of the pointP at the time T2, which is predicted at the time T1,

P1min is the minimum value (end point) that satisfies “f1(P)≧predetermined radiopaque dye density”, and

P1max is the maximum value (leading point) that satisfies “f1(P)+g1(P)>predetermined radiopaque dye density”.

However, the density g1 (P) is predicted based on f1 (P), assuming thatthe radiopaque dye density distribution does not relatively change in ashort time.

As described above, according to the second embodiment, the next timingof radiation imaging is determined based on the moving speed calculatedby a radiopaque dye moving speed prediction unit 205 and the radiopaquedye density distribution detected by a radiopaque dye densitydistribution detection unit 204. In the second embodiment, the longesttiming at which the sum of the radiopaque dye density distributionsacquired from the image obtained by the latest radiation imaging and theimage to be obtained by the next radiation imaging is always equal to orhigher than a predetermined radiopaque dye density is employed.

In the first and second embodiments, the present invention has beendescribed using angiography using a radiopaque dye. However, the presentinvention is also applicable to contrastradiography except forangiography and, for example, to contrastradiography of an organ using aradiopaque dye such as barium. In an organ, the radiopaque dye moves onits walls, unlike angiography. However, it is possible to calculate themoving distance based on the “point with the highest radiopaque dyedensity” of two images, as in angiography.

Other Embodiments

The embodiments have been described above in detail. The presentinvention can also take a form of, for example, a system, apparatus,method, program, or storage medium. More specifically, the presentinvention is applicable to a system including a plurality of devices oran apparatus including a single device.

The present invention also incorporates a case in which the functions ofthe above-described embodiments are achieved by supplying a softwareprogram to the system or apparatus directly or from a remote site andcausing the computer of the system or apparatus to read out and executethe supplied program codes. In this case, the supplied program is acomputer program corresponding to the illustrated flowcharts of theembodiments.

Hence, the program codes themselves which are installed in a computer toimplement the functional processing of the present invention alsoimplement the present invention. That is, the present invention alsoincorporates the computer program itself to implement its functionalprocessing.

In this case, the program can take any form such as an object code, aprogram to be executed by an interpreter, or script data to be suppliedto the OS as long as the functions of the program are available.

Examples of a computer-readable storage medium to supply the program area floppy® disk, hard disk, optical disk, magnetooptical disk, MO,CD-ROM, CD-R, CD-RW, magnetic tape, nonvolatile memory card, ROM, andDVD (DVD-ROM, DVD-R).

The following program supply method is also available. A client computermay connect to a homepage on the Internet via a browser to download thecomputer program of the present invention from the homepage to arecording medium such as a hard disk. In this case, the downloadedprogram may a compressed file including an automatic installationfunction. The program codes contained in the program of the presentinvention may be divided into a plurality of files so that the user candownload the files from different homepages. That is, a WWW server whichcauses a plurality of users to download the program file to cause acomputer to implement the functional processing of the present inventionis also incorporated in the present invention.

The program of the present invention may be encrypted, stored in astorage medium such as a CD-ROM, and distributed to users. Any user whosatisfies predetermined conditions can download key information fordecryption from a homepage via the Internet. The user can execute theencrypted program by using the key information and install the programin the computer.

The functions of the above-described embodiments are implemented whenthe computer executes the readout program. The functions of theabove-described embodiments may also be implemented in cooperation with,for example, the OS running on the computer based on the instructions ofthe program. In this case, the OS or the like partially or whollyexecutes actual processing so that the functions of the above-describedembodiments are implemented.

The functions of the above-described embodiments may also be partiallyor wholly implemented by writing the program read out from the recordingmedium in the memory of a function expansion board inserted into thecomputer or a function expansion unit connected to the computer. In thiscase, the program is written in the function expansion board or functionexpansion unit, and then, the CPU of the function expansion board orfunction expansion unit partially or wholly executes actual processingbased on the instructions of the program.

As described above, according to the present invention, the radiationirradiation timing is controlled in accordance with a change in themoving speed of a radiopaque dye. It is therefore possible to obtain aDSA image by appropriate irradiation while suppressing the irradiationdose and the amount of radiopaque dye injection.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2007-211501, filed Aug. 14, 2007, which is hereby incorporated byreference herein in its entirety.

1. A radiation imaging apparatus comprising: a detection unit adapted todetect a density distribution of an image formed by a radiopaque dyefrom an image obtained by radiation imaging; a prediction unit adaptedto calculate a moving speed of the image formed by the radiopaque dye onthe basis of a moving amount of the density distribution detected bysaid detection unit in two images obtained by radiation imaging and aninterval between radiographing times of the two images; and adetermination unit adapted to determine a next timing of radiationimaging on the basis of the moving speed calculated by said predictionunit and the density distribution detected by said detection unit. 2.The apparatus according to claim 1, wherein said prediction unitcalculates, as a moving amount of the density distribution, a movingamount of a position with a highest density in the density distributiondetected by said detection unit in the two images.
 3. The apparatusaccording to claim 1, wherein said determination unit determines thenext timing of radiation imaging to joint portions having not less thana predetermined radiopaque dye density in the density distribution whenthe density distribution detected by said detection unit moves at themoving speed calculated by said prediction unit.
 4. The apparatusaccording to claim 1, wherein said determination unit determines thenext timing of radiation imaging to, at a connection portion between thedensity distribution of an image obtained by latest radiation imagingand the density distribution of an image after movement, make a sum ofthe density distributions equal a predetermined radiopaque dye densitywhen the density distribution detected by said detection unit moves atthe moving speed calculated by said prediction unit.
 5. A method ofcontrolling a radiation imaging apparatus, comprising: a detection stepof detecting a density distribution of an image formed by a radiopaquedye from an image obtained by radiation imaging; a prediction step ofcalculating a moving speed of the image formed by the radiopaque dye onthe basis of a moving amount of the density distribution detected in thedetection step in two images obtained by radiation imaging and aninterval between radiographing times of the two images; and adetermination step of determining a next timing of radiation imaging onthe basis of the moving speed calculated in the prediction step and thedensity distribution detected in the detection step.
 6. The methodaccording to claim 5, wherein in the prediction step, a moving amount ofa position with a highest density in the density distribution detectedin the detection step in the two images is calculated as a moving amountof the density distribution.
 7. The method according to claim 5, whereinin the determination step, the next timing of radiation imaging isdetermined to joint portions having not less than a predeterminedradiopaque dye density in the density distribution when the densitydistribution detected in the detection step moves at the moving speedcalculated in the prediction step.
 8. The method according to claim 5,wherein in the determination step, the next timing of radiation imagingis determined to, at a connection portion between the densitydistribution of an image obtained by latest radiation imaging and thedensity distribution of an image after movement, make a sum of thedensity distributions equal a predetermined radiopaque dye density whenthe density distribution detected in the detection step moves at themoving speed calculated in the prediction step.
 9. A computer-readablestorage medium storing a computer program which causes a computer tocontrol a radiation imaging apparatus, the computer program causing thecomputer to execute: a detection step of detecting a densitydistribution of an image formed by a radiopaque dye from an imageobtained by radiation imaging; a prediction step of calculating a movingspeed of the image formed by the radiopaque dye on the basis of a movingamount of the density distribution detected in the detection step in twoimages obtained by radiation imaging and an interval betweenradiographing times of the two images; and a determination step ofdetermining a next timing of radiation imaging on the basis of themoving speed calculated in the prediction step and the densitydistribution detected in the detection step.